Nutrient signaling integrates and coordinates gene expression, metabolism and growth. In multicellular organisms, growth factors and hormones are ineffective in growth promotion without the support of nutrient signaling networks. However, surprisingly little is known about the primary nutrient signaling mechanisms in plants and animals. Plants play a central role in bridging the conversion of inorganic nitrogen to organic nitrogen in the global nitrogen cycle by assimilating inorganic nitrate to generate amino acids, nucleic acids, and organic nitrogen-carbon molecules, which are essential to build and sustain lives from plants and humans. Despite the fundamental and multifaceted regulatory roles of nitrate in gene expression, metabolism, growth and development, the molecular and cellular mechanisms of nitrate signaling remain mostly elusive in multicellular plants. Hampered by gene redundancy and mutant lethality, classical genetic screens had limited success for identifying key nitrate signaling components in plants over the past two decades. By taking integrated molecular, cellular, biochemical, functional genomic, chemical genetic and systems analyses, we have discovered a surprising molecular link between specific Ca2+-sensor protein kinases (CPKs) and the NODULE INCEPTION-LIKE PROTEIN (NLP) transcription factors as the primary regulators of the nitrate-signaling network in plants. Our research has demonstrated the unique role of nitrate as a central signaling molecule in transcriptome reprograming and shoot- root coordination to shape organ biomass and architecture. We propose to build on our new findings and innovative experimental platforms to elucidate the molecular and cellular basis of the nutrient-growth network that orchestrates system-wide transcription and modulates plant developmental processes. We will implement complementary strategies and methodologies to advance our understanding of nutrient signaling mechanisms via elucidating the biological functions of Ca2+-CPK signaling in nutrient-coupled transcription responses essential to all life forms. We will analyze the nitrate sensing and signaling mechanism by transporters/sensors, and uncover the cellular and molecular mechanism of novel nitrate signaling components. The proposed research on unraveling the signaling mechanisms mediated by the nitrate-CPK-NLP relay, transporter/sensor, and novel nutrient regulators will establish new paradigms in nutrient-mediated transcriptional and developmental regulation with sustained scientific impact beyond plant biology. Aim 1. Elucidate the nitrate-CPK-NLP signaling relay in plant nutrient-growth network Aim 2. Analyze nitrate nutrient sensing and signaling mechanisms Aim 3. Uncover the molecular and cellular action of novel nitrate signaling components